The purposes of this study are to describe in biochemical terms how Ehrlich ascites cells interact with lipids contained in the extracellular fluid, to determine how the availability of extracellular lipids influences lipid metabolism within the cells, and to investigate whether changes in the dietary fat fed to the host mouse will influence the fatty acid composition of the Ehrlich cell membrane lipids. The chemical and physical properties of the Ehrlich ascites plasma lipoproteins will be characterized. In addition, the factors that regulate the concentration and composition of lipoproteins in the ascites fluid and in the blood plasma of the mouse host will be investigated. The utilization of radioactive triglycerides added to the ascites plasma lipoproteins will be compared in vitro in culture as opposed to in vivo in the mouse peritoneal cavity. Cell membrane fatty acid composition will be investigated in relation to the fat composition of the mouse diet. Free fatty acid binding to a soluble cellular protein will be investigated. Attempts will be made to isolate and characterize the fatty acid receptor of Ehrlich cell membranes.